Hydrocarbon feeds can be reacted in a hydroprocessing zone where a number of reactions take place, including hydrocracking, hydrotreating, hydrogenation, and desulfurization. The hydroprocessing zone is typically followed by a stripper column, where the hydroprocessing zone effluent is separated into a stripper overhead stream and a stripper bottoms stream. In some processes, the stripper column bottoms is sent to a fractionation column, where it is separated into a fractionation column bottoms stream and a naphtha overhead stream. Other streams, such as light gas oil and heavy gas oil streams, can also be separated out in the fractionator, if desired. The naphtha overhead stream is recovered. The naphtha overhead stream includes naphtha, H2S, and, in some cases, water.
The H2S generated during desulfurization reactions in the hydroprocessing zone is removed predominantly in the stripper column. Although the stripper column is designed to remove H2S to the level of parts per billion (ppb) in the stripper bottoms stream, small amounts of H2S slip through into the fractionator. The H2S becomes concentrated to a level of parts per million (ppm) in the fractionator overhead liquid stream. ASTM D-4952-09 (Doctor Test) is often used as an indicator for the presence of H2S in the overhead naphtha stream. An H2S level of 1 weight ppm (wppm) can result in the naphtha not meeting the Doctor Test. If the naphtha does not meet the Doctor Test, it cannot be sent directly to the naphtha pool for storage. Consequently, the H2S must be removed from the naphtha overhead stream using a secondary processing system.
In many units, the H2S is removed using a caustic (NaOH) wash and a sand filter. However, many refiners do not want to use caustic because of the hazards associated with handling it and problems related to disposing of the spent caustic.
Alternatively, the naphtha may be sent to a downstream stabilizer/splitter combination for removal of light petroleum gas. The H2S can be removed along with the light petroleum gas. However, this equipment increases the cost of the process.
Therefore, it would be desirable to provide alternative processes for removing H2S from naphtha.